ETBC: COLLABORATIVE RESEARCH: MASS-DEPENDENT AND INDEPENDENT MERCURY ISOTOPE FRACTIONATION DURING MICROBIAL METHYLATION AND REDOX TRANSFORMATIONS OF MERCURY IN NATURAL WATERS

ETBC：合作研究：天然水中汞的微生物甲基化和氧化还原转化过程中质量依赖和独立的汞同位素分馏

• 批准号: 0952108
• 负责人: Joel Blum
• 金额: $ 26.24万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-06-01 至 2014-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0952108&HistoricalAwards=false
• 关键词: ETBC; COLLABORATIVE; RESEARCH; MASS; DEPENDENT

Intellectual merit: The proposed research is based on recent achievements by the PIs and others, and seeks to expand the PIs? on-going studies of isotopic fractionation during microbial and abiotic Hg transformations. During the last five years the PIs have shown that: (i) Mass dependent isotopic fractionation (MDF) occurred during the microbial reduction of ionic mercury (Hg[II]) by several bacterial strains that possess the enzyme mercuric reductase and MDF also occurred during microbial methylmercury (MeHg) degradation; (ii) Photoreduction of Hg(II) and photodegradation of MeHg caused MDF as well as mass independent fractionation (MIF) of up to 2?. Varying amounts of MIF (denoted as Ä199Hg and Ä201Hg) recorded in freshwater and marine fish tissue suggested different extents of photo degradation of MeHg prior to its incorporation into the aquatic food web. These results along with large variations in natural samples documented by the Blum lab and others, strongly suggest that the isotopic composition of Hg has the potential for distinguishing between different sources of Hg(0) emissions and pathways of Hg(II) reduction and MeHg degradation.To date, the PIs? studies have focused on Hg redox transformations and MeHg degradation. Yet, the bioaccumulation of MeHg in aquatic food webs has a profound effect on human and ecosystem health and the examination of whether or not isotope fractionation occurs during methylation of Hg is, therefore, a high priority. If significant fractionation occurs during formation of MeHg and is modulated by different environmental conditions and by the nature of the methylating processes, tools for distinguishing sources and pathways of MeHg in the environment may become available and enhance the management of Hg contaminated ecosystems. The first objective of the proposed study is the examination of isotopic fractionation during Hg methylation by sulfate and iron reducing bacteria to test the hypothesis that microbial Hg methylation results in significant MDF, but not in MIF. The second objective is the investigation ofhow environmental variables, which define freshwater and marine environments, impact MIF and MDF during Hg redox transformations to test the hypothesis that photochemical reduction, oxidation and demethylation will imprint diagnostic MDF and MIF signatures on reaction substrates and products. Finally, Hg isotopic fractionation during transformation pathways mediated by an important component of aquatic ecosystems, phototrophic planktonic organisms, has not been examined to date. The third objective addresses this lack of knowledge by testing the hypothesis that intracellular Hg(II) reduction and MeHg degradation in phytoplankton incubated in the light will result in MDF and possibly MIF. Broader Impact: The proposed research activity will continue to lay the groundwork for a new approach or the identification of sources, sinks, and pathways of Hg transformations in impacted ecosystems. This approach has the potential to significantly enhance understanding of Hg biogeochemistry on temporal and spatial scales ranging from molecular mechanisms, to ecosystems, to global cycles, and to the geological record. As ecosystem Hg contamination remains a major public health concern, this project will support implementation of sound environmental practices to reduce Hg contamination and exposure. The proposed research will train a postdoctoral fellow in the application of stable isotope-based approaches in geobiology and ecosystem processes. In addition, undergraduate and graduate students will be integrated into the project, exposing them to cutting edge concepts and technologies, which are at the interface between biology, geology and ecosystem sciences. It is at this interface that importantparadigm-shifting, research advances are being made. Undergraduate students will assist with the analytical geochemistry as part of senior thesis research projects and PhD dissertation projects. Results will be published and disseminated broadly.

学术价值：拟议的研究基于 PI 和其他人的最新成果，旨在扩大 PI 正在进行的微生物和非生物汞转化过程中同位素分馏的研究，PI 已表明：（ i) 在几种具有汞酶的细菌菌株对离子汞 (Hg[II]) 进行微生物还原的过程中，发生了质量依赖性同位素分馏 (MDF)还原酶和 MDF 也在微生物甲基汞 (MeHg) 降解过程中发生；(ii) Hg(II) 的光还原和 MeHg 的光降解导致 MDF 以及高达 2? 的质量无关分馏 (MIF)（表示为不同量）。淡水和海水鱼类组织中记录的 ä199Hg 和 ä201Hg）表明甲基汞在其释放之前发生了不同程度的光降解。这些结果以及 Blum 实验室和其他人强烈记录的自然样本的巨大差异表明，Hg 的同位素组成有可能区分不同的 Hg(0) 排放源和 Hg 途径。 (II) 还原和甲基汞降解。迄今为止，PIs 研究主要集中在汞氧化还原转化和甲基汞降解上，然而，甲基汞在水生食物网中的生物累积对汞具有深远的影响。因此，人类和生态系统的健康以及汞甲基化过程中是否发生同位素分馏的检查是当务之急。区分环境中甲基汞的来源和途径的工具可能会出现，并加强对汞污染的生态系统的管理。拟议研究的第一个目标是检查汞甲基化过程中的同位素分馏。第二个目标是研究定义淡水和海洋环境的环境变量在汞氧化还原转化过程中如何影响 MIF 和 MDF。光化学还原、氧化和去甲基化将在反应底物和产物上留下诊断性 MDF 和 MIF 特征的假设最后，在重要介导的转化途径中汞同位素分馏。迄今为止，尚未对水生生态系统的组成部分（光养浮游生物）进行研究，第三个目标通过检验在光下培养的浮游植物中细胞内汞（II）减少和甲基汞降解将导致 MDF 并可能导致 MDF 的假设来解决这一知识的缺乏。 MIF。更广泛的影响：拟议的研究活动将继续为新方法或确定受影响生态系统中汞转化的途径奠定基础。加强对汞生物地球化学在时间和空间尺度上的理解，从分子机制到生态系统，到全球循环和地质记录。由于生态系统汞污染仍然是一个主要的公共卫生问题，该项目将支持实施良好的环境实践，以减少汞污染。汞污染和暴露。拟议的研究将培训一名博士后研究员在地球生物学和生态系统过程中应用基于稳定同位素的方法。此外，本科生和研究生将被纳入该项目，让他们接触到前沿技术。概念和技术是生物学、地质学和生态系统科学之间的交叉点，正是在这个交叉点上，本科生将协助分析地球化学，作为高级论文研究项目和博士学位的一部分。论文项目的结果将被出版并广泛传播。